1. Field of the Invention
This invention relates to automated apparatus for unwinding and splicing multiple rolls of web.
2. Description of the Related Art
A number of manufacturing processes involve webs that are initially received in roll form and are subsequently unwound from the roll for further processing. Newspapers, for example, are made by unwinding a roll of paper and then cutting the paper into sheets after a printing operation. Other examples of processes involving webs include methods for making photographic film, pressure sensitive tapes, magnetic audio, video and data storage tapes, as well as a variety of other products.
In many processes that involve unwinding of a web from a roll, the web is relatively thin and the roll represents a relatively long length of web. As a result, such web rolls are exhausted only infrequently and the unwinding process can be continued for a relatively long length of time without interruption until the roll is depleted and replaced by another roll. Paper stock for newspapers, for example, is relatively thin and a large number of newsprint sheets can be printed before the roll is exhausted.
However, other web processes involve webs that are relatively thick. As can be appreciated, a roll of relatively thick web is much shorter in length than a roll of relatively thin web for a given diameter of roll. Consequently, the rolls of thick web used in high-speed operations are quickly exhausted and must be replaced at relatively frequent intervals.
Orthopedic splinting and casting tape, such as Scotchcast.TM. brand and Scotchcast Plus.TM. brand synthetic casting tape (from 3M) is made by coating a porous knit fiberglass backing with a water curable polyurethane resin. An improved apparatus for making splinting or casting tape is described in a pending U.S. patent application entitled "Web Coating Apparatus" Ser. No 08/301,258, filed on even date herewith. However, the fiberglass backing is relatively thick (for example, about 0.5 mm) and as a result the rolls of the backing are quickly exhausted and must be frequently replaced during the coating process.
In operations involving coated webs, it is often desirable to avoid interruption of the coating process in order to help insure that the coating has a uniform thickness that does not unduly vary along the length of the web. Some fluids used to coat webs begin to cure relatively quickly when exposed to the atmosphere and may exhibit an increase in viscosity during the length of time necessary to change the roll. When the coating process is resumed with a new roll, the initial portion of the roll may have to be discarded because the change in fluid viscosity may have adversely affected the thickness, coverage or other characteristic of the coating on the initial, leading edge portion of the web that is unwound from the roll.
Web unwinding and splicing apparatus for two rolls of relatively thick web is known in the art for enabling processing of the web with fewer interruptions that would be observed for single roll unwinding apparatus. One such unwinding and splicing apparatus includes two unwind spindles located opposite one another, with a roll of web received on each spindle. When the web of one roll is exhausted, a photocell detector senses the absence of additional web from that roll and triggers a splicing mechanism. The splicing mechanism includes a pair of parallel push plates that push the trailing edge of the unwinding roll into contact with a leading edge of the standby roll. Double sided adhesive tape or other coupling means is provided to connect the webs together. An operator then places another web roll on the now-vacant spindle.
There is a continuing need in the art to decrease expenses associated with web processing operations. In this regard, there is in particular a need for an improved automated unwinding and splicing mechanism that requires less operator attention than the presently known unwinding and splicing apparatus so that the operator is free to carry out other, more productive tasks.